In this detailed review article, he and Bhavna Abbi at the War Related Illness and Injury Study Center in East Orange, NJ, lay out the evidence to date suggesting that the underlying pathophysiology of fibromyalgia may be different than that of ME/CFS.

Although the full text of the article (abstract below) is fee-based, Dr. Natelson indicates the identified differences fall into these categories:

And the work continues. Dr. Natelson has extended a request to our site visitors, asking for ME/CFS and fibromyalgia volunteers to take part in several current studies designed to fill in further pieces of the puzzle. (See "Dr. Natelson recruiting for CFS & FM studies in NYC.")

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Abstract:
Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are medically unexplained syndromes that can and often do co-occur. For this reason, some have posited that the two are part of the same somatic syndrome-examples of symptom amplification.

This hypothesis would suggest that few differences exist between the two syndromes.

To evaluate this interpretation, we have searched the literature for articles comparing CFS to FM, reviewing only those articles which report differences between the two.

This review presents data showing differences across a number of parameters - implying that the underlying pathophysiology in CFS may differ from that of FM.

We hope that our review encourages other groups to look for additional differences between CFS and FM.

By continuing to preserve the unique illness definitions of the two syndromes, clinicians will be able to better identify, understand and provide treatment for these individuals.

Dear Dr - I am astonished that in Sept 2012, you are unaware that FM is a DISTINCT ILLNESSS , found familiarly, hereditarily, with pre-disposition genetic factors. The CAUSE IS RESEARCHED AS ENDOGENOUSLY BEGINNING WITH THE DYSFUNCTIONING OF THE CNS + ANS, WHICH IN TURN DYSFUNCTIONS ALL OTHER BRAIN AND BODY SYSTEMS. THE 'UNKNOWN GENE' IS SITUATED IN THE PITUITARY GLAND (DR RIBIE EMG STUDIES 2007!) These studies, ie brain + THYMUS GLAND SHOWING ALL WITH FM HAVE 4CMS INSTEAD OF 8CMS FEEDING THE SENSORY NERVOUS SYSTEM. TOO THE PINEAL GLAND FEEDER OF MELATONIN, IS INSUFFICIENT ALWAYS, THUS INSOMNIA, RESTLESS SLEEP FROM PAIN WITHOUT ABILITY TO GO TO ALPHA B/REM SLEEP WITHOUT MUCH HELP FROM SUPPLEMENTAL EG GAGA, MELATONIN, SAMe. One can thus be born with ACTIVE Primary Fm, or begin with signs/symptoms therof from the earliest age. My patients range from 3 months to acknowledgement by MEDICAL DRS age 75!!!
CFS IS CHARACTERISED BY EXTEME FATIGUE, NO PAIN ( DEFINITIVE PAIN IN FM), AND OTHER BRAIN SYSTEM EG ENDOCRINE DYSFUNCTIONALITY, LOW TONE MUSCULAR SYSTEM WHEN TOO MANY STRESSORS HAVE OVERCOME THE PATIENT. ME GENERALLY ADJOINS CFS, AND CAN BE PART OF FM AS WELL.
SHARON LEVIN. HEAD OF FM SOUTHERN AFRICA www.fibromyalgiasa.co.za